public void onSensorChanged(SensorEvent event) {
        float azimuth = event.values[0];
        Location currentLoc = getHelper().getCurrentLocation();
        if(currentLoc == null || cardinal == null || cardinal.getLocation() == null) {
            return;
        }

        azimuth = (float) Math.toDegrees(azimuth);
        GeomagneticField geoField = new GeomagneticField(
                (float) currentLoc.getLatitude(),
                (float) currentLoc.getLongitude(),
                (float) currentLoc.getAltitude(),
                System.currentTimeMillis());

        azimuth += geoField.getDeclination(); // converts magnetic north into true north
        float bearing = currentLoc.bearingTo(cardinal.getLocation()); // (it's already in degrees)
        float direction = azimuth - bearing;
        direction = -direction;
        if(compass != null) {
            compass.setDirection(direction);
        }
}

public void onDraw(Canvas canvas) { //
    int height = this.getHeight();  //
    int width = this.getWidth();

    canvas.rotate(direction, width / 2, height / 2); //
    super.onDraw(canvas); //
}